In the past, to avoid a collision of data which are transmitted from wireless stations in a wireless network, it has been checked by means of carrier sense whether or not there exists a vacancy in a channel. For example, each wireless station performs carrier sense before data transmission, and, when power greater than or equal to a threshold value is detected, each wireless station determines that the channel is in a busy state and stops transmission. On the other hand, when power smaller than the threshold value is detected, each wireless station determines that the channel is in an idle state and starts transmission.
However, even when carrier sense is performed, a collision of data that is undetectable by means of carrier sense may occur between wireless stations, resulting in decrease in the success rate of transmission. For example, when a transmitting wireless station transmits data to a receiving wireless station, a collision of data occurs between the transmitting wireless station and a wireless station that is located within a communication range of the receiving wireless station and is unable to detect transmission performed by the transmitting wireless station by means of carrier sense. That is, a collision of data occurs between the transmitting wireless station and a wireless station (hereinafter referred to as a hidden terminal) at which received power from the transmitting wireless station is less than or equal to the threshold value. In this case, the same packet is retransmitted to suppress decrease in the rate of successful arrival of data.
However, in a wireless station (hereinafter referred to as a bottleneck wireless station) on which traffic is concentrated, such as a wireless station located at a route of a tree-topology network, a collision of data due to hidden terminals may occur frequently and retransmission of data may be repeated. As a result, traffic is increased, which causes congestion of a network and decreases the rate of successful arrival of data.
As a technology of avoiding such congestion, the technology of uniformly reducing the amount of data to be transmitted when any of the transmitting wireless stations detects congestion and gradually increasing the amount of data to be transmitted when the recovery from congestion is detected is disclosed. Moreover, technology of avoiding congestion is also disclosed in which the probability of occurrence of a collision due to hidden terminals is estimated based on traffic information and the number of wireless stations that are considered as hidden terminals so as to select a wireless station which is less likely to be affected by the hidden terminals and to avoid a wireless station that is likely to cause congestion.
Japanese Laid-open Patent Publication No. 2008-227854 and “TCP Congestion Control”, RFC5681, IETF, 2009.9, are examples of related art.